The present invention relates to an optical fiber array substrate used in an optical device connecting a plurality of optical fibers and has securing grooves for receiving and positioning a plurality of optical fibers, and also to a method for producing the same.
In late years, there has been an increased demand for high-capacity and high-speed optical communication networks and optical devices of the optical fiber array type have been brought to attention. Typically, in such devices, a plurality of optical fibers are aligned by using a substrate having linear V-grooves, and such substrate is fabricated by a fabrication method such as press working, shaving or grinding of a plate material, or directional etching of a silicon single-crystal plate material.
However, in order to satisfy a severe dimensional accuracy required for optical fiber array substrates by means of the fabrication method as mentioned in the above, it is required to grind V-grooves precisely with high angular accuracy one by one, to finish the V-grooves with desired height and desired interval therebetween. Therefore, there are problems that the methods require many steps and are complicated, hence non-defective fraction is not increased so that costs are expensive.
In an optical fiber array substrate manufactured according to the method as described above, since the surfaces of linear V-grooves are rough and the shape of the regions between the V-grooves are too sharp, optical fibers may be damaged when mounting and also the optical fiber array substrate itself may be apt to be damaged or chipped. Therefore, it becomes concerned that the substrate may be decreased in breakage resistance to be broken. Moreover, the V-grooves, which are finished after a lot of work, may be damaged during working process or following cleaning process. Further, the bottom or top of the V-grooves may be cracked during grinding process and the like, and thereby breakage resistance of the substrate may be lowered. Thus, the optical fiber array substrate may often be broken during handling so that the yield is lowered. Therefore the production efficiency of such optical fiber array substrates is so low that they are not suitable for mass production.
Japanese Patent Laid-Open Publication No. Hei 2-13913 discloses a fabrication method of an optical fiber array substrate in which a glass base material is heated and softened to be drawn (i.e. to be drawn and formed) to a dimension of 1/10. However, since the base material actually is softened and deformed during the drawing process, it is difficult to keep the shape and to control the dimensional accuracy. As a result, the shape of the V-grooves becomes to be deformed, particularly the shape of the outside V-grooves becomes to be deformed significantly. In addition, the heights of the V-grooves become to be not uniform due to variations thereof. Thus, such optical fiber array substrates do not wear for applications requiring high accuracy. More specifically, in a substrate formed by the conventional drawing process, the surface of the base material where the V-grooves are formed is slightly elongated when heated and softened, so that the central portion of the surface is deformed to cave in the order of several micrometers. As a result of this deformation, the V-grooves in the central portion become to be lower than the V-grooves in the peripheral portion by several micrometers. When optical fibers are arranged in such V-grooves, the heights at the centers of the cores of the optical fibers become to vary by several micrometers, so that it is very difficult to fabricate a high precision substrate with V-grooves.
Further, in a conventional optical fiber array substrate 1 as shown in FIG. 9(A), outside ridges 2d and 2e defining outermost V-grooves 2a and 2b of optical fiber securing V-grooves 2 are greatly different in shape from inside ridges 2c. Therefore, when optical fibers 4 are adhered to the optical fiber array substrate 1 by the use of a thermosetting adhesive, or when they have been arranged as an optical fiber array, a difference in heat history between the outside optical fibers 4a, 4b and the inside optical fibers 4c which are supported in the V-grooves 2 is generated due to a difference in heat capacity between the outside ridges 2d, 2e and the inside ridges 2c, which will be a factor to lower the reliability of the optical fiber array.
Furthermore, in the conventional optical fiber array substrate 1 as shown in FIG. 9(B), when the optical fibers 4 are held down by a plate 5 and fixed with an adhesive 6, if the amount of the adhesive is too small, there is a problem that some of the optical fibers 4 will not be fixed completely, because of the adhesive 6 not being distributed sufficiently to the fixing portions for all of the optical fibers. On the contrary, if the amount of the adhesive is too large, the adhesive 6 will run off from the side of the substrate 1, as shown in FIG. 9(C), so that troublesome tasks such as scraping the run-off adhesive 6a or polishing the sides of the substrate 1 will be required to comply with the predetermined dimension. Therefore, there is a problem that the amount of adhesive is required to be controlled strictly.